Cyllindrical helical core geometry for heat exchanger

ABSTRACT

A heat exchanger includes a first fluid manifold extending along a first fluid axis from a first fluid inlet to a first fluid outlet. The first fluid manifold includes first fluid inlet and outlet headers, and a helical core section. The inlet header is disposed to branch the first fluid inlet into a plurality of first fluid branches, and the outlet header is disposed to combine the plurality of first fluid branches into the first fluid outlet. The core section fluidly connects the inlet header to the outlet header via a plurality of helical tubes, such that each helical tube corresponds to one of the plurality of first fluid branches.

CROSS-REFERENCE TO RELATED APPLICATION(S)

This application claims the benefit of U.S. Provisional Application No.62/815,847 filed Mar. 8, 2019 for “CYLLINDRICAL HELICAL CORE GEOMETRYFOR HEAT EXCHANGER” by A. Becene, G. Ruiz, F. Feng, M. Maynard, M. Doe,M. Hu, and E. Joseph.

BACKGROUND

The present disclosure is related generally to heat exchangers and moreparticularly to heat exchanger core designs.

Heat exchangers can provide a compact, low-weight, and highly effectivemeans of exchanging heat from a hot fluid to a cold fluid. Heatexchangers that operate at elevated temperatures, such as those used inmodern aircraft engines, often have short service lifetimes due tothermal stresses, which can cause expansion and cracking of the fluidconduits. Thermal stresses can be caused by mismatched temperaturedistribution, component stiffness, geometry discontinuity, and materialproperties (e.g., thermal expansion coefficients and modulus), withregions of highest thermal stress generally located at the interface ofthe heat exchanger inlet/outlet and core.

A need exists for heat exchangers with increased heat transfer, reducedpressure loss and vibration excitation, and improved performance underthermal stresses.

SUMMARY

In one aspect, the present disclosure is directed toward a heatexchanger that includes a tubular inlet, a tubular outlet, and a core.The core fluidically connects the tubular inlet to the tubular outletvia a plurality of tubes. Each of the tubes has a helical shape and iscircumferentially displaced from each of the others of the plurality oftubes.

In another aspect, the present disclosure is directed toward a heatexchanger that includes a first fluid manifold extending along a firstfluid axis from a first fluid inlet to a first fluid outlet. The firstfluid manifold includes first fluid inlet and outlet headers, and ahelical core section. The inlet header is disposed to branch the firstfluid inlet into a plurality of first fluid branches, and the outletheader is disposed to combine the plurality of first fluid branches intothe first fluid outlet. The helical core section fluidly connects theinlet header to the outlet header via a plurality of helical tubes, suchthat each helical tube corresponds to one of the plurality of firstfluid branches.

The present summary is provided only by way of example, and notlimitation. Other aspects of the present disclosure will be appreciatedin view of the entirety of the present disclosure, including the entiretext, claims, and accompanying figures.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is schematized side view of a heat exchanger with a helical core.

FIG. 2 is an exaggerated perspective side view of the heat exchanger ofFIG. 1, in a compressed state.

While the above-identified figures set forth one or more embodiments ofthe present disclosure, other embodiments are also contemplated, asnoted in the discussion. In all cases, this disclosure presents theinvention by way of representation and not limitation. It should beunderstood that numerous other modifications and embodiments can bedevised by those skilled in the art, which fall within the scope andspirit of the principles of the invention. The figures may not be drawnto scale, and applications and embodiments of the present invention mayinclude features and components not specifically shown in the drawings.

DETAILED DESCRIPTION

A heat exchanger with a rotationally symmetric helical core is presentedherein. This helical core is made up of a plurality of structurallyindependent, circumferentially distributed and helical tubes. Thesetubes can be distributed in a cylindrically distributed springarrangement. The helical geometry of the core increases heat exchangerfunctional length and surface area as a function of the total axiallength of the core, and provides structural compliance that allows thecore to serve as a spring to relieve thermal and other stresses from theheat exchanger and adjacent (connecting) flow elements.

FIG. 1 is a schematized side view of heat exchanger 10, which includesfirst fluid manifold 12 and second fluid guide 14. First fluid manifold12 includes inlet header 16, outlet header 18, and core section 20.Inlet header 16 forks from inlet passage 22 into a plurality of inletheader branches 24, and outlet header 18 recombines outlet headerbranches 26 into outlet passage 28. Core 20 is formed of a plurality ofstructurally independent helical tubes 30 that each extend from aseparate inlet header branch 24 to a separate outlet header branch 26.

During operation of heat exchanger 10, hot fluid flow F1 is provided toinlet header 16, flows through core 20, and exits through outlet header18. Thermal energy is transferred from hot fluid flow F1 to coolingfluid flow F2 as hot fluid flow F1 passes through core 20. It will beunderstood by one of ordinary skill in the art that the disclosedindependent cold flow structure can be tailored for use with a widevariety of core geometries and is not limited to the embodiments shown.Furthermore, although the present disclosure refers to some flow as“cold” and other as “hot,” the present geometry can more generally beapplied to any two fluid flows in a heat exchange relationship, e.g.wherein F1 and F2 are exchanged i.e. as cold and hot flows,respectively.

As illustrated in FIG. 1, heat exchanger 10 is oriented substantiallysymmetrically along a fluid axis A, which connects extends from inletpassage 22 to outlet passage 28. In this embodiment, axis A is astraight line defining a primary flow direction of hot fluid flow F1through first fluid manifold 12. In variations on the depictedembodiment, however, heat exchanger 10 can extend along a contoured(non-straight) axis, e.g. due to space constraints.

Headers 16, 18 distribute and receive fluid, respectively, substantiallyevenly across core 20. Specifically, inlet header 16 splits into inletheader branches 24, and outlet header 18 recombines from header branches26. In the illustrated embodiment, header 16 is a successively fractallybranching manifold with multiple stages of branches, each narrowing incross-sectional flow area with respect to the previous stage of lessnumerous branches, finally terminating in the full count of outletheader branches 22 as the narrowest and most axially distant from inletpassage 22. More specifically, the present figures illustrate each stageof header 16 branching rotationally symmetrically about axis A into aneven number of tubes evenly circumferentially distributed across acommon plane transverse to axis A. More generally, however, header 16can be of any shape capable of distributing fluid from a single sourceat inlet passage 22 across the multitude of separate helical tubes 30 ofcore 20. The illustrated embodiment, however, advantageously reducespressure drop and provides additional mechanical compliance along axisA, within header 16.

As depicted in FIG. 1, header 18 substantially mirrors header 16, acrosscore 20. In at least some embodiments, headers 16, 18 and core 20 areall formed monolithically. More generally, all components of heatexchanger first fluid manifold 12 can be formed partially or entirely byadditive manufacturing. For metal components (e.g., Inconel, aluminum,titanium, etc.) exemplary additive manufacturing processes include butare not limited to powder bed fusion techniques such as direct metallaser sintering (DMLS), laser net shape manufacturing (LNSM), electronbeam manufacturing (EBM). For polymer or plastic components,stereolithography (SLA) can be used. Additive manufacturing isparticularly useful in obtaining unique geometries (e.g., varied coretube radii, arcuate core tubes, branched inlet and outlet headers) andfor reducing the need for welds or other attachments (e.g., betweenheaders 16, 18 and core 20). However, other suitable manufacturingprocess can be used. For example, header and core elements can in someembodiments be fabricated separately and joined via later manufacturingsteps.

Second fluid guide 14 is illustrated schematically in FIG. 1. Secondfluid guide 14 can be included in some embodiments to constrain coolingfluid flow F2. Second fluid guide 14 is illustrated as a bafflesurrounding mechanically unconnected to first fluid manifold 12. Inother embodiments, second fluid guide 14 can have additional sub-layersor separations to further channel cooling fluid flow F2 through andacross first fluid manifold 12. In still other embodiments, by contrast,second fluid guide 14 can be omitted altogether, and first fluidmanifold 12 directly exposed to an unconstrained environment of coolingfluid flow F2. Second fluid guide 14 need not closely match the geometryof first fluid manifold 12, but can in some embodiments parallel atleast some aspects of the geometry of first fluid manifold, e.g. to moreclosely capture core section 20 as a whole. In the illustratedembodiment, second fluid guide 14 channels cooling fluid flow F2 in adirection substantially antiparallel (i.e. parallel to but opposite) hotfluid flow F1. In other embodiments, second fluid guide 14 can insteaddirect cooling fluid flow F2 in a direction transverse to F1, e.g. in across-flow direction.

The majority of heat transfer enabled by heat exchanger 10 isaccomplished within core section 20. Core section is formed by aplurality of separate, structurally independent helical tubes 30. Eachhelical tube 30 has a helical or spring-like geometry, extending axiallyand turning in common about fluid axis A. Helical tubes 30 aredistributed circumferentially about axis A, such that each helical tube30 is substantially identical to all other tubes 30, but shiftedcircumferentially relative to adjacent tubes. All tubes 30 are depictedas cross-sectionally distributed in a circular array across a planeorthogonal to fluid axis A. More generally, tubes 30 can be distributedin any array with rotational symmetry about fluid axis A, e.g. inelliptical or cloverleaf patterns. Circular symmetry in the distributionof tubes 30 permits all tubes 30 to have identical geometry, withcorrespondingly identical and therefore uniform fluid flow and heattransfer characteristics. Asymmetric arrangements of tubes 30, however,may be advantageous in tight space constraints, or where cooling fluidflow F2 is non-uniform. The spacing between adjacent helical tubes 30 isprimarily circumferential, which provides a substantially uniform gapspacing between all adjacent tubes 30, so as to promote even airflow F2therebetween. All helical tubes 30 can have a substantially identicaland uniform inner diameter with a circular cross-section, resulting inequal cross-sectional areas. In the illustrated embodiment, the spacingbetween adjacent helical tubes 30 is greater than this inner diameter.In general, the rotational symmetry of helical tubes 30 within core 20permits flow paths within headers 16, 18 to be substantially equal inlength, for greater uniformity in the distribution of fluid flow F1across tubes 30 relative to geometries with no such symmetry, or othersymmetry types.

The helical shape of tubes 30 of core 20 serves several functions.First, helical tubes 30 have no sharp corners or interfaces (e.g. withheaders 16, 18), and consequently reduce unnecessary pressure losses.Second, helical tubes 30 are compliant along axis A, acting as a springcapable of deforming to accommodation expansion or axial translation ofadjacent components. In particular, helical tubes 30 can be capable ofcompliantly deforming along axis A so as to accommodate thermal growthof headers 16, 18, and/or translation of headers 16, 18 due to thermalgrowth of adjacent (upstream or downstream) components. This mechanicalcompliance provided by core 20 allows heat exchanger to betterdistribute and weather thermal and other mechanical stresses. FIG. 2 isan exaggerated (not to scale) perspective side view of heat exchanger 10illustrating a compressed state of first fluid manifold 12. FIG. 2illustrates the performance of core section 20 under such compression.

In at least some embodiments, helical core 20 is significantly lesscompliant laterally, i.e. in dimensions transverse to fluid axis A. Thisincreased lateral stiffness provides first fluid manifold 12 withresonant frequencies of oscillation transverse to the first fluid flowthat are greater than the range of operating frequencies of asurrounding engine or other components for at least its three highestamplitude natural frequencies, for example, so as to avoid excitationwithin the expected environment of heat exchanger 10. The generallycircular cross-section of each tube 30 contributes to this increasedlateral stiffness. The helical geometry of tubes 30 also providesgreater fluid flow length within each tube 30, and correspondinglygreater surface area exposed to cooling fluid flow F2. The overallpassage length of each tube 30 can, for example, be double the axiallength of core 30, or more. Helical tubes 30 can introduce additionalturbulence to fluid flows F1, F2, for additional heat transfer.

In view of the above, in comparison to conventional straight-lineconnected channels, core 20 provides heat exchanger 10 with improvedaxial compliance to handle thermal stresses, increased lateral stiffnessto avoid potentially harmful resonance conditions, and increased surfacearea exposed to cooling fluid flow F2 for greater heat exchange, allwith only modest pressure losses from inlet passage 22 to outlet passage28. Furthermore, the geometry of core 20 is symmetrical along two axes(axial and radial), and can consequently improve the uniformity ofstress distribution across first fluid manifold 12.

Discussion of Possible Embodiments

The following are non-exclusive descriptions of possible embodiments ofthe present invention.

A heat exchanger comprising: a tubular inlet; a tubular outlet; and acore fluidically connecting the tubular inlet to the tubular outlet viaa plurality of tubes each having a helical shape and circumferentiallydisplaced from each of the others of the plurality of tubes.

A heat exchanger comprising: a fluid manifold extending along a firstfluid axis from a first fluid inlet to a first fluid outlet, the firstfluid manifold comprising: an inlet header disposed to fork the firstfluid inlet into a plurality of first fluid branches distributedcircumferentially about the first fluid axis; an outlet header disposedto combine the plurality of first fluid branches into the first fluidoutlet; and a helical core section fluidly connecting the inlet headerto the outlet header via a plurality of cylindrically arranged helicaltubes, each helical tube corresponding to one of the plurality of firstfluid branches.

The heat exchanger of the preceding paragraph can optionally include,additionally and/or alternatively, any one or more of the followingfeatures, configurations and/or additional components:

A further embodiment of the foregoing heat exchanger, wherein each ofthe plurality of helical tubes is structurally independent from allothers of the plurality of helical tubes, such that the plurality ofhelical tubes are mechanically connected to each other only at the inletheader and the outlet header.

A further embodiment of the foregoing heat exchanger, wherein each ofthe plurality of helical tubes extends axially along andcircumferentially about the first fluid axis.

A further embodiment of the foregoing heat exchanger, wherein the firstfluid axis extends linearly from the first fluid inlet passage to thefirst fluid outlet passage, and wherein the first fluid inlet and thefirst fluid outlet are themselves oriented along the first fluid axis.

A further embodiment of the foregoing heat exchanger, wherein each ofthe plurality of helical tubes is mechanically separated from adjacentof the plurality of helical tubes by a circumferential and axial gap.

A further embodiment of the foregoing heat exchanger, wherein astructural rigidity of the first fluid manifold along the first fluidaxis is less than along any radial dimension with respect to the firstfluid axis.

A further embodiment of the foregoing heat exchanger, wherein the firstfluid manifold is situated in an environment with a known range ofoperating frequencies, and wherein the first fluid manifold has at leasta highest amplitude natural resonance frequency of oscillationtransverse to the first fluid axis that is greater than the known rangeof operating frequencies.

A further embodiment of the foregoing heat exchanger, wherein each ofplurality of helical tubes has a total passage length at least doubleits extent along the first fluid axis.

A further embodiment of the foregoing heat exchanger, wherein thehelical core section forms a spring shape extending between the inletheader and the outlet header, wherein the spring shape is principallycompliant along the first fluid axis.

A further embodiment of the foregoing heat exchanger, wherein thehelical core section is capable of compliantly deforming to accommodateaxial growth of the inlet header and outlet header.

A further embodiment of the foregoing heat exchanger, further comprisinga second fluid flow structure disposed to direct a second fluid toimpinge on the first fluid manifold, wherein the second fluid flowstructure is configured to direct the second fluid generally along adirection from the first fluid outlet to the first fluid inlet.

A further embodiment of the foregoing heat exchanger, wherein the inletheader branches the first fluid inlet passage into a first number N offirst fluid branches, and wherein the plurality of helical tubescomprises N helical tubes even distributed circumferentially to form acylindrical arrangement with a circumferential angular separation of360°/N.

A further embodiment of the foregoing heat exchanger, wherein theentirety of the first fluid manifold is formed monolithically as asingle structure.

A further embodiment of the foregoing heat exchanger, wherein all of theplurality of helical tubes have identical flow area.

A further embodiment of the foregoing heat exchanger, wherein all of theplurality of helical tubes have a circular cross-section with a commondiameter.

Summation

Any relative terms or terms of degree used herein, such as“substantially”, “essentially”, “generally”, “approximately” and thelike, should be interpreted in accordance with and subject to anyapplicable definitions or limits expressly stated herein. In allinstances, any relative terms or terms of degree used herein should beinterpreted to broadly encompass any relevant disclosed embodiments aswell as such ranges or variations as would be understood by a person ofordinary skill in the art in view of the entirety of the presentdisclosure, such as to encompass ordinary manufacturing tolerancevariations, incidental alignment variations, alignment or shapevariations induced by thermal, rotational or vibrational operationalconditions, and the like.

While the invention has been described with reference to an exemplaryembodiment(s), it will be understood by those skilled in the art thatvarious changes may be made and equivalents may be substituted forelements thereof without departing from the scope of the invention. Inaddition, many modifications may be made to adapt a particular situationor material to the teachings of the invention without departing from theessential scope thereof. Therefore, it is intended that the inventionnot be limited to the particular embodiment(s) disclosed, but that theinvention will include all embodiments falling within the scope of theappended claims.

1. A heat exchanger comprising: a tubular inlet; a tubular outlet; and acore fluidically connecting the tubular inlet to the tubular outlet viaa plurality of tubes each having a helical shape and circumferentiallydisplaced from each of the others of the plurality of tubes.
 2. A heatexchanger comprising: a fluid manifold extending along a first fluidaxis from a first fluid inlet to a first fluid outlet, the first fluidmanifold comprising: an inlet header disposed to fork the first fluidinlet into a plurality of first fluid branches distributedcircumferentially about the first fluid axis; an outlet header disposedto combine the plurality of first fluid branches into the first fluidoutlet; and a helical core section fluidly connecting the inlet headerto the outlet header via a plurality of cylindrically arranged helicaltubes, each helical tube corresponding to one of the plurality of firstfluid branches.
 3. The heat exchanger of claim 2, wherein each of theplurality of helical tubes is structurally independent from all othersof the plurality of helical tubes, such that the plurality of helicaltubes are mechanically connected to each other only at the inlet headerand the outlet header.
 4. The heat exchanger of claim 2, wherein each ofthe plurality of helical tubes extends axially along andcircumferentially about the first fluid axis.
 5. The heat exchanger ofclaim 2, wherein the first fluid axis extends linearly from the firstfluid inlet passage to the first fluid outlet passage, and wherein thefirst fluid inlet and the first fluid outlet are themselves orientedalong the first fluid axis.
 6. The heat exchanger of claim 2, whereineach of the plurality of helical tubes is mechanically separated fromadjacent of the plurality of helical tubes by a circumferential andaxial gap.
 7. The heat exchanger of claim 2, wherein a structuralrigidity of the first fluid manifold along the first fluid axis is lessthan along any radial dimension with respect to the first fluid axis. 8.The heat exchanger of claim 7, wherein the first fluid manifold issituated in an environment with a known range of operating frequencies,and wherein the first fluid manifold has at least a highest amplitudenatural resonance frequency of oscillation transverse to the first fluidaxis that is greater than the known range of operating frequencies. 9.The heat exchanger of claim 2, wherein each of plurality of helicaltubes has a total passage length at least double its extent along thefirst fluid axis.
 10. The heat exchanger of claim 2, wherein the helicalcore section forms a spring shape extending between the inlet header andthe outlet header, wherein the spring shape is principally compliantalong the first fluid axis.
 11. The heat exchanger of claim 2, whereinthe helical core section is capable of compliantly deforming toaccommodate axial growth of the inlet header and outlet header.
 12. Theheat exchanger of claim 2, further comprising a second fluid flowstructure disposed to direct a second fluid to impinge on the firstfluid manifold, wherein the second fluid flow structure is configured todirect the second fluid generally along a direction from the first fluidoutlet to the first fluid inlet.
 13. The heat exchanger of claim 2,wherein the inlet header branches the first fluid inlet passage into afirst number N of first fluid branches, and wherein the plurality ofhelical tubes comprises N helical tubes even distributedcircumferentially to form a cylindrical arrangement with acircumferential angular separation of 360°/N.
 14. The heat exchanger ofclaim 2, wherein the entirety of the first fluid manifold is formedmonolithically as a single structure.
 15. The heat exchanger of claim 2,wherein all of the plurality of helical tubes have identical flow area.16. The heat exchanger of claim 16, wherein all of the plurality ofhelical tubes have a circular cross-section with a common diameter.